(i) Technical Field
The present invention relates to focal plane shutters and optical apparatuses provided with the same.
(ii) Related Art
There is known a focal plane shutter: including a board including an opening; a leading blade and a trailing blade opening and closing the opening; an actuator driving the trailing blade; and a drive member driving the trailing blade by receiving driving force of the actuator. Such a focal plane shutter is disclosed in Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2002-043227.
The drive member that drives the trailing blade is swingably provided in the board. Further, the drive member is provided with a drive pin. The drive member swings such that the drive pin moves within an escape slot formed in the beard. This restricts the swinging range of the drive member. There is a case where a buffering member is provided at an end portion of the escape slot in order to absorb the impact when the drive pin abuts with the end portion of the escape slot. In this case, the following problem may occur.
In a charging operation before an exposure operation, the leading blade move to close the opening while the trailing blade is maintained away from the opening. In the state where the trailing blade is positioned away from the opening, the drive member that drives the trailing blade is maintained in abutment with the buffering member. In a case where the drive member is maintained in abutment with the buffering member for a predetermined period, the drive member might press the buffering member and a stop position of the drive member might be positionally displaced from the desired position. In this case, the rotational range of the drive member in the exposure operation is increased, and the moving distance of the trailing blade is increased. In this case, the exposure period might be longer than the desired period.
Further, when the drive member is maintained in abutment with the buffering member, the buffering member and the drive member might adhere to each other with weak force. In this case, in the exposure operation, the timing when the drive member moves out of contact with the buffering member might be delayed from the desired timing. In this case, the exposure period might also be longer than the desired period. In such as way, the exposure period might be varied.
Furthermore, in a case where the buffering member is not provided at the end portion of the escape slot, the following problem may occur. In the state where the trailing blade is positioned away from the opening before the exposure operation, the drive member that drives the trailing blade is maintained in abutment with the and portion of the escape slot as a portion of the board. When this state is maintained the drive member and the end portion of the escape slot might adhere to each other with weak force. In this case, the timing when the drive member moves out of contact with the end portion of the escape slot might also be delayed from the desired timing, and the exposure period might also be longer than the desired period. In such a way, the exposure period might be varied.
The above problem might occur, in a case where a focal plane shutter where the leading blade closes the opening and trailing blade moves away from the opening in an initial state before pushing a release button and the exposure operation is performed by pushing the release button.